Useful Application of "Reduce Number of Generated Combinations" Function 

Example 1: Selecting leading variable actions

According to DIN EN 1990, fire resistance design should be performed in the accident design situation. It is necessary to check the national application document to decide whether to use the frequent value (ψ_1,1 Q_k,1) or the quasi-permanent value (ψ_2,1 Q_k,1). In this case, the information can be found in the National Annex to DIN EN 1991‑1‑2 under the Nationally Determined Parameters (NDP) to 4.3.1(2). It says that for components of which the main action is the wind, the frequent value (ψ_1,1 Q_k,1) is to be used. The other cases apply the quasi‑permanent value (ψ_2,1 Q_k,1).

In RFEM/RSTAB, you can choose between both values in the combination expressions. For a fire situation, you can select the combination expression "Accident - psi 1.1 – Eq. 6.11c" and only define Wind as the leading action under "Select Leading Variable Actions". Thus, only wind with a frequent value and the remaining variable actions with a quasi‑permanent value are considered in the combinations.

Example 2: Reducing the number of load cases

For serviceability limit state design, the British National Annex to BS EN 1993‑1‑1 (steel construction) requires the characteristic combination without a ratio of permanent loads (see BS EN 1993‑1‑1/NA.2.23). This means that the deflection components w_g,inst due to self‑weight are to be reduced. In this case, you can use the "Reducing number of load cases ..." option. In the load cases to be considered, all load cases are selected except self‑weight. Click [Yes] to confirm the message that appears. Then, the combinations are displayed without considering the self‑weight.